外国人的经典UG教程.pdf

Kenneth Youssefi Mechanical Engineering 082802, page 1 Product Design Process A complex process requiring a cross-functional team consisting of not only design engineers but also individuals from manufacturing, financing, marketing, and etc. Traditional Design Process Kenneth Youssefi Mechanical Engineering 082802, page 2 Concurrent Design Process Involves coordination of the technical and non-technical functions of design and manufacturing within a business. Kenneth Youssefi Mechanical Engineering 082802, page 3 Product life cycle: ?Design phase ?Manufacturing phase ?Product usage phase ?Disposal phase ?Reduction in cost and lead time and improvements in product quality must be sought from all areas of a product- life cycle. ?The design phase is most critical; o Determines the product success or failure in the market place o Has a direct impact on product cost, quality, manufacturing processes, future maintenance cost, and cost to dispose of the product after usage Approximately, 80% of the product cost is fixed at the design stage, and it is easier and less costly to change the design at the early design phase. Kenneth Youssefi Mechanical Engineering 082802, page 4 Computer Integrated Design and Manufacturing Companies must deliver products to customers at the minimum possible cost, the best possible quality, and the minimum lead time starting from the product conception stage to final delivery, service and disposal. The core of computer technology includes: ? Computer-Aided Design (CAD) Geometric modeling ? Computer-Aided Manufacturing (CAM) ? Computer-Aided Engineering (CAE) Analysis Kenneth Youssefi Mechanical Engineering 082802, page 5 3D Modeling There are three basic types of three-dimensional computer geometric modeling methods: ?Wireframe modeling ?Surface modeling ?Solid modeling Kenneth Youssefi Mechanical Engineering 082802, page 6 Wireframe Modeling ?Contains information about the locations of all the points (vertices) and edges in space coordinates. ?Each vertex is defined by x, y, z coordinate. ?Edges are defined by a pair of vertices. ?Faces are defined as three or more edges. ?Wireframe is a collection of edges, there is no skin defining the area between the edges. E E E E V V V V 1 2 3 4 2 3 1 4 EDGE VERTEX Kenneth Youssefi Mechanical Engineering 082802, page 7 Advantages of Wireframe Models ?The only lines seen are the intersections of surfaces ?Can more quickly and efficiently convey information than multiviews ?Requires less computation and memory ?Contain most of the information needed to create surface, solid and higher order models ?Can be used for finite element analysis ?Can be used as input for NC machines to generate parts Kenneth Youssefi Mechanical Engineering 082802, page 8 Disadvantages of Wireframe Models ?Do not represent an actual solids (no surface and volume) ?Cannot model complex curved surfaces ?Cannot be used to calculate dynamic properties ?Ambiguous views (ambiguous orientation) A B C D A B CD A C D ?have problems with uniqueness Kenneth Youssefi Mechanical Engineering 082802, page 9 Example of wireframe lack of uniqueness Kenneth Youssefi Mechanical Engineering 082802, page 10 Surface Models A surface model represents the skin of an object, these skins have no thickness or material type. ?Surface models define the surface features, as well as the edges, of objects. ?A mathematical function describes the path of a curve (parametric techniques) ?Surfaces are copied, moved and rotated as single entities ?Surfaces are edited as single entities (editing surfaces are rather difficult, easier to start over) Kenneth Youssefi Mechanical Engineering 082802, page 11 Advantages of Surface Models ?Eliminates much ambiguity and non-uniqueness present in wireframe models by hiding lines not seen ?Renders the model for better visualization and presentation, objects appear more realistic ?Provides the surface geometry for computer-aided manufacturing (CAM), NC (numerically controlled) machines ?Provides the geometry needed by the manufacturing engineer for mold and die design ?Can be used to design and analyze complex free- formed surfaces of ship hulls, airplane fuselages and car bodies ?Surface properties such as roughness, color and reflectivity can be assigned and demonstrated ?Can be used to approximate intersections Kenneth Youssefi Mechanical Engineering 082802, page 12 Disadvantages of Surface Models ?Provides no information about the inside of an object ?Curved surfaces need a fine mesh to be accurate ?Provides wrong results if mesh is too coarse ?Complicated computation, depending on the number of surfaces Kenneth Youssefi Mechanical Engineering 082802, page 13 Solid Models In the solid modeling, the solid definitions include vertices (nodes), edges, surfaces, weight, and volume. The model is a complete and unambiguous representation of a precisely enclosed and filled volume. Kenneth Youssefi Mechanical Engineering 082802, page 14 Advantages of Solid Models ?Has all the advantages of surface models (uniqueness, non-ambiguous, realistic, surface profile) plus volumetric information. ?Allows the designer to create multiple options for a design. ?2D standard drawings, assembly drawing and exploded drawings are generated form the model. ?Can easily be exported to different Finite Element Methods programs for analysis ?Can be used in newly manufacturing techniques; computer integrated manufacturing (CIM), computer aided manufacturing (CAM) and design for manufacturability (DFM) Kenneth Youssefi Mechanical Engineering 082802, page 15 ?Mass properties of an object can be easily obtained Total mass Centroid (mass center)- point through which the weight of the body effectively acts. Mass moment of inertia - used to compute the force required to rotate an object. Area moment of inertia - used to calculate stress Product of mass moment of inertia - used to determine forces causing the motion of an object with respect to two different 2-D planes Principal moment of inertia - highest mass moment of inertia at the centroid along one of the axes. Radius of gyration - the distance at which the entire mass of the object should be concentrated to obtain the same mass properties. Kenneth Youssefi Mechanical Engineering 082802, page 16 Disadvantages of Solid Modeling ?More intensive computation than wireframe and surface modeling ?Requires more powerful computers (faster with more memory), not a problem any more Kenneth Youssefi Mechanical Engineering 082802, page 17 Three Methods of Creating Solid Models 1. Boundary Representation (B-rep) (finite element programs) 2. Constructive Solid Geometry (CSG) (Unigraphics, AutoCAD 3D modeler, ) 3. Parametric Modeling (Unigraphics, SolidWorks, AutoCAD Inventor, Pro-Engineering, ) Kenneth Youssefi Mechanical Engineering 082802, page 18 Methods of Creating Solid Models 1. Boundary Representation (B-rep) ?A solid model is formed by defining the surfaces that form its boundary (edges and surfaces) ?The face of a B-rep represents an oriented surface, there two sides to the surface; solid side (inside) and void side (outside), unlike faces in a wireframe. ?B-rep model is created using Euler operation ?Many Finite Element Methods (FEM) programs use this method. Allows the interior meshing of the volume to be more easily controlled. Kenneth Youssefi Mechanical Engineering 082802, page 19 Methods of Creating Solid Models 2. Constructive Solid Geometry (CSG) ?CSG defines a model in terms of combining basic and generated (using sweeping operation) solid shapes, B-rep defines a model in terms of edges and surfaces ?CSG uses Boolean operations to construct a model (George Boole, 1815-1864, invented Boolean algebra) ?There are three basic Boolean operations: Union (Unite, join) - the operation combines two volumes included in the different solids into a single solid Subtract (cut) - the operation subtracts the volume of one solid from the other solid object Intersection - the operation keeps only the volume common to both solids Kenneth Youssefi Mechanical Engineering 082802, page 20 Primitive Solids and Boolean Operations The basic primitive solid set typically includes: cube, rectangular prism (block), cylinder, triangular prism (wedge), cone, sphere and torus (donut) Kenneth Youssefi Mechanical Engineering 082802, page 21 Primitive Solids The location of the insertion base or base point and default axes orientation. Kenneth Youssefi Mechanical Engineering 082802, page 22 Methods of Creating Solid Models 3. Parametric Modeling ?Parametric is a term used to describe a dimensions ability to change the shape of model geometry if the dimension value is modified. ?Feature-based is a term used to describe the various components of a model. For example, a part can consists of various types of features such as holes, fillet, and chamfers. SolidWorks is a featured-based, parametric, solid modeling design program Unigraphics Modeling application combines CSG and parametric approaches to modeling Kenneth Youssefi Mechanical Engineering 090402, page 1 Design Intent ?Design intent is how your model will react when dimension values are changed. ?In parametric modeling programs, dimensions control the model. Example: The drawing below shows the intension of the designer that the chamfer should have a flat area measuring 2.5 inches and that it should start at a point 1.25 inches from the base of the drawing. These parameters are what the designer deemed significant for this practical model. Remember that the placement of dimensions is very important because they are being used to drive the shape of the geometry. If the 2.5 in. vertical dimension increases, the 2.5 in. flat across the chamfer will be maintained, but the its angle will change. Kenneth Youssefi Mechanical Engineering 090402, page 2 In this drawing, what is important to the designer is the vertical and horizontal dimensions of the chamfer, rather than the flat of the chamfer. In the last drawing, the designer calls for a specific angle for the chamfer. In this case the angle of the chamfer should be dimensioned. Kenneth Youssefi Mechanical Engineering 090402, page 3 Notes ?Keep in mind that dimensioning scheme can be changed at any time. You are not locked into a specific design. You can also design without dimensioning, rough out a sketch, and then later go back and fully define it. ?Do not be concerned with dimensioning to datum or stacked tolerances in the part. Those issues can be addressed in the drawing layout. Be more concerned with your design intent. Kenneth Youssefi Mechanical Engineering 090402, page 4 Boolean Versus Parametric Modelers The ability to go back on some earlier stage in the design process and make changes by editing a sketch or changing some dimensions is extremely important to a designer. This is a main advantage of a parametric (Unigraphics, SolidWorks, Inventor, ProE) over a non-parametric modeler (AutoCAD 3D modeler Boolean operation) Example: Lets assume that you want to design a part consisting of a ring with a certain thickness and a series of counterbore holes along the perimeter. Kenneth Youssefi Mechanical Engineering 090402, page 5 Boolean operation ?Create the initial base part by extruding the profile in a particular direction. Or create two cylinders and subtract the small one from the large one ?Create the solid geometry that will become the counterbore holes. ?Position the pattern about the perimeter of the base part. Locating the holes is critical to creating an accurate solid model. Kenneth Youssefi Mechanical Engineering 090402, page 6 ?Subtract the pattern from the base part to create the actual holes. What would happen if you had to come back to this part to change the size of the counterbore holes? Since Boolean operation was used to create the part, it would be very time consuming to edit, much easier to re-create the part with new holes. This is specially true for complex parts. Kenneth Youssefi Mechanical Engineering 090402, page 7 Parametric modeler (UG, SolidWorks) ?Create the initial base part by extruding the profile in a particular direction (same as before). ?Create the counterbore as a feature. Features can be fillets, chamfers, bosses or holes, extrudes or revolved, and so on. It does not matter if you are taking material away or adding it. There are no Boolean operations. ?The next step would be to pattern the hole. The pattern would actually be considered a feature in itself, and would have its set of parametric variables, such as the number of copies and the angle between copies. Kenneth Youssefi Mechanical Engineering 090402, page 8 The model created would be identical to the one created using Boolean operation, but with intelligence build into the model. The true power of parametric modelers shine through when design changes need to be made. The design change is made by simply changing a dimension. If the dimensions of the counterbore hole were changed, the rest of the patterned holes would change as well. Kenneth Youssefi Mechanical Engineering 090402, page 9 3D Coordinate Systems 1. Cartesian Coordinates ?Used most frequently in 3D modeling ?Defined by three mutually perpendicular axes (X, Y and Z) ?The Right Hand Rule Kenneth Youssefi Mechanical Engineering 090402, page 10 3D Coordinate Systems 2. Cylindrical Coordinates ?Useful in designs involving circular shapes or patterns ?Points defined in terms of “r” from the origin and angle ? between r and +X axis (measured in the plane perpendicular to Z axis (XY plane) ?The transformation equations to convert to Cartesian coordinates are: X = r cos(?), Y = r sin(?), Z = z Kenneth Youssefi Mechanical Engineering 090402, page 11 3D Coordinate Systems 3. Spherical Coordinates ?Points defined in terms of “r” radial distance from origin, angle ? between r and +X (measured in XY plane and angle ? between r and +Z (measured in ZX plane) ?The transformation equations to convert to Cartesian coordinates are: X = r cos(?) sin(?), Y = r sin(?) sin(?), Z = r cos(?) Kenneth Youssefi Mechanical Engineering 090402, page 12 Absolute and Relative Coordinate Values ?XYZ (absolute) - global coordinate system, origin at 0,0,0 ?XYZ (relative) - local coordinate system, origin defined by user ?Point B of the small box located relative to point A of the large box Unigraphics An Interactive CAD/CAM/CAE System ? The CAD functions automate the normal engineering, design, and drafting ? The CAM functions provide NC (Numeric Control) programming for modern machine tools ? The CAE functions provide the analyses of the design model to check if the part can satisfy design requirements in mechanical, thermal, or dynamic aspects ? Unigraphics functions are divided into “applications” Unigraphics Coordinate systems ?Absolute Coordinate System (ABS) Defines 0,0,0 (in X, Y, and Z) in model space and it is fixed, used as a general